The present invention relates to a starting control circuit for a high pressure lamp.
In public lighting installations, high pressure (HP) lamps, in particular HP sodium lamps are commonly used which are individually controlled by means of a photocell mounted on the lantern itself.
As such a lamp approaches the end of its life, the necessary voltage to be applied to the lamp to keep it working increases from its nominal value to a higher value, for example from 110 V to 130-140 V. In addition, the arc voltage becomes higher when the temperature of the lamp increases so that the working threshold voltage may exceed a value above which the lamp extinguishes. However, as the lamps thereafter cools, it may be started again because the starting circuit continuously provides starting pulses and the above threshold voltage decreases due to the decrease of temperature. This can be repeated during the whole working period of the lighting installation and is known as the "cycling" phenomenon.
Such defective lamps cause an actual discomfort and are not easily detected despite regular inspection of the public lighting installations due to their intermittent working.